public class MyLinkedList {
    static class ListNode {
        int val;
        ListNode prev;
        ListNode next;
        public ListNode(int val){
            this.val=val;
        }
    }
    public ListNode head;
    public ListNode last;
    public void addFirst(int data){
        ListNode node = new ListNode(data);
        if(head == null){
            head = node;
            last = node;
        }else{
            node.next = head;
            head.prev = node;
            head = node;
        }
    }
    //尾插法
    public void addLast(int data){
        ListNode node = new ListNode(data);
        if(head == null){
            head = node;
            last = node;
        }else{
            last.next = node;
            node.prev = last;
            last = node;
        }
    }
    //任意位置插入,第一个数据节点为0号下标
    public void addIndex(int index,int data){
        if(index <0 && index >= size()){
            System.out.println("下标不合法");
            return;
        }
        if(isEmpty()){
            System.out.println("链表为空");
            return;
        }
        if(index == 0){
            addFirst(data);
            return;
        }
        if(index == size()){
            addLast(data);
            return;
        }
        ListNode node = new ListNode(data);
        ListNode cur = head;
        while(index!=0){
            cur = cur.next;
            index--;
        }
        node.next = cur;
        node.prev = cur.prev;
        cur.prev.next = node;
        cur.prev = node;
    }
    private boolean isEmpty(){
        if(head == null){
            return true;
        }
        return false;
    }
    //查找是否包含关键字key是否在单链表当中
    public boolean contains(int key){
        if(head == null){
            return false;
        }
        ListNode cur = head;
        while (cur!=null){
            if(cur.val == key){
                return true;
            }
            cur = cur.next;
        }
        return false;
    }
    //删除第一次出现关键字为key的节点
    public void remove(int key){
        if(head == null){
            return;
        }
        ListNode cur = head;
        while(cur != null){
            if(cur.val == key){
                if(cur == head){
                    head = head.next;
                    if(head != null) {
                        head.prev = null;
                    }
                }else if(cur == last){
                    last = last.prev;
                    last.next = null;

                }else{
                    cur.prev.next = cur.next;
                    cur.next.prev = cur.prev;

                }
                return;
            }
            cur = cur.next;
        }
    }
    //删除所有值为key的节点
    public void removeAllKey(int key){
        if(head == null){
            return;
        }
        ListNode cur = head;
        while(cur != null){
            while(cur != null&&cur.val == key){
                if(cur == head){
                    head = head.next;
                    if(head!=null) {
                        head.prev = null;
                    }
                }else if(cur == last){
                    last = last.prev;
                    last.next = null;
                }else{
                    cur.prev.next = cur.next;
                    cur.next.prev = cur.prev;
                }
                cur = cur.next;
            }
            if(cur == null){
                last = null;
                return;
            }
            cur = cur.next;
        }
    }
    //得到单链表的长度
    public int size(){
        ListNode cur = head;
        int count = 0;
        while(cur != null){
            count++;
            cur = cur.next;
        }
        return count;
    }
    public void display(){
        ListNode cur = head;
        while(cur != null) {
            System.out.print(cur.val+" ");
            cur = cur.next;
        }
    }
    public void clear(){
        ListNode cur = head;
        while (cur != null){
            ListNode curnext = cur.next;
            cur.next=null;
            cur.prev=null;
            cur = curnext;
        }
    }
}
